Changes in Operations Australia - GRail (Details) AUD in Thousands, $ in Thousands, carload in Millions			3 Months Ended
	Dec. 01, 2016 AUD wagon Train_Sets locomotive $ / AUD	Dec. 01, 2016 USD ($)	Mar. 31, 2017 AUD carload	Mar. 31, 2017 USD ($) carload	Dec. 31, 2016 AUD	Mar. 31, 2016 USD ($) $ / AUD	Dec. 31, 2016 USD ($)	Dec. 01, 2016 USD ($) wagon Train_Sets locomotive $ / AUD
Proceeds from Previous Acquisition | $				$ 2,935		$ 0
Foreign currency exchange rate | $ / AUD	0.74					0.72		0.74
Noncontrolling Interest, Ownership Percentage by Parent	51.10%							51.10%
Goodwill | $				1,149,582			$ 1,125,596
Australian Senior Credit Facility [Member]
Debt Instrument, Term					5 years
Proceeds from Issuance of Debt					AUD 690,000
Australian Term Loan [Member] | Credit agreement [Member]
Long-term Debt, Gross					250,000
MIRA [Member]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	48.90%							48.90%
GRail [Member]
Business Acquisition, Effective Date of Acquisition	Dec. 01, 2016	Dec. 01, 2016
Payments to Acquire Businesses, Gross	AUD 1,140,000	$ 844,900
Proceeds from Previous Acquisition			AUD 3,800	2,900
Business Combination, Consideration Transferred	AUD 1,300,000
Debt Issuance Costs, Gross					19,800
Business Combination, Acquisition Related Costs					AUD 13,200
Business Combination, Rail Haulage Contract, Term of Contract	20 years	20 years
Business Combination, Rail Haulage Contract, Period of Minimum Guaranteed Volumes	18 years	18 years
Entity Number of Train Sets Owned or Leased | Train_Sets	9							9
Entity Number of Locomotives Owned or Leased | locomotive	30							30
Entity Number of Wagons Owned or Leased | wagon	894							894
Business Combination, Integration Related Costs | $				$ 100
Accounts receivable	AUD 1,556							$ 1,153
Materials and supplies	411							305
Property and equipment	279,592							207,206
Goodwill	415,959							308,267
Total Assets	1,332,518							987,530
Accounts payable and accrued expenses	5,796							4,296
Deferred income tax liabilities, net	190,551							141,217
Net assets	1,136,171							$ 842,017
GRail [Member] | Customer Contracts [Member]
Finite-lived Intangible Assets Acquired	AUD 635,000	$ 470,599
GRail [Member] | Steam Coal [Domain]
Annual Tonnes Hauled | carload			40	40